Take a look at Replace Field Contents with the calculation option.
If your 3rd layout specifies LeaveComp in Show Records from in Layout Setup..., you can use three Replace Field Contents operations to copy the data from the global fields into the matching non global field for all records currently in the found set. Replace Field Contents can be done manually and also via a script.
This is not something you can Undo and it can modify hundreds of records in one go, so make back up copies before testing this method.
Thank you for the reply. I will try and play with the Replace Field command and report back my progress.
Happy New Year.